An important parameter in selecting a potentiometer is the taper. They typically come in one of three styles, linear, audio, and reverse audio. A linear taper pot will be at 50% of its total resistance when the pot is rotated half way. An audio taper pot will be at 50% of its resistance when the shaft is rotated to about 85% of its CW travel. A reverse audio taper pot will be a 50% if its resistance at about 15% of its travel. For an application like a speed control, you want a linear pot so the operating range isn;t compressed
As to type of resistance element, a wirewound pot is the the least sisceptab;le to wear from the wiper. The two issues with wire wound pots are they are limited to lower resistance values and the resistance necessarily increase in step as the wiper slides from one winding to the next. This can be a problem if you want tight resolution. Other types of resistance elements include carbon film, conductive plastic, and cermet. Of these, the carbon film is least reliable but cheapest. It is best relegated to set it and forget it type application. Cermet pots are reliable. I haven't evaluated any conductive plastic pots so I can't comment on their reliability.
Another parameter is the power rating. As with any resistor, when the power rating is exceeded, the pot will overheat and can fail prematurely. This shouldn't be an issue with the OP though.
Finally, comes the resistance value. If a pot is operating as a variable resistance or rheostat, this is important. Too low a value will limit operation while too high a value will limit the useful range of the rheostat. Operated as a potentiometer or voltage divider, the resistance is less critical as the voltage out it equal to the product of the voltage in and the fraction of rotation and independent of resistance. Resistance can come into play regarding the associated electronic but usually isn't a problem as long as values are reasonably close to the design value.
edit: I should add mechanical characteristics such as mounting type, shaft style, and single or multi turn. Also, open design vs. enclosed vs sealed.